[MPlayer-users] How to find out "timestamps" of a mpeg stream?

[Josef Wolf]

Hallo!

I need some way to find out how long (in seconds) a mpeg stream
lasts. My first try (in perl) was:

    my $f = "stream.mpg";
    my $start=undef;
    my $end=undef;
    open(L,"mplayer -nosound -vo null -ao null -speed 100 $f|") or die;
    while (my $l=<L>) {
        for my $l1 (split (/\015/, $l)) {
            if ($l1=~/^V:\s*([\d,]+)/) {
                $end = $1;
                $end =~ s/\,/./;
                $start = $end if $end ne "0.0" && !defined $start;
            }
        }
    }
    close L;
    print "Length: ", $end-$start, "\n";

This code does the job, but it is somewhat slooow because it needs
to decode the whole stream. So I came up with the following:

    my $f = "stream.mpg";
    my $pos = (-s $f) - 1024*1024;
    $pos=0 if $pos<0;
    my $start = &frametime ("-frames 1 $f");
    my $end   = &frametime ("-sb $pos $f");
    print "Length: ", $end-$start, "\n";

    sub frametime {
        my ($par) = @_;
        my $sec=undef;
        open(L,"mplayer -nosound -vo null -ao null -speed 100 $par|") or die;
        while (my $l=<L>) {
            for my $l1 (split (/\015/, $l)) {
                if ($l1=~/^V:\s*([\d,]+)/) {
                    $sec = $1;
                    $sec =~ s/\,/./;
                }
            }
        }
        close L;
        return $sec;
    }

This too does the job. In addition, it is much faster. But starting
at 1MB before the end of file seems to be strange. What would be a
good choice to guarantee that at least one complete frame would be
"played"?

Anyone an idea?

-- 
-- Josef Wolf -- jw at raven.inka.de --